Cell_Biology_of_the_Respiratory_System_2023.11.02_Student (1).pptx

Cell Biology of the Respiratory System Steven J. Ontiveros, MBA, PhD Objectives • Describe cells of the epithelium of the nasal cavity, trachea, and bronchioles, including specialized cells such as the olfactory sensory cells, Club (Clara) cells, and Pulmonary Ionocytes. • Provide a general descri...

Cell Biology of the Respiratory System Steven J. Ontiveros, MBA, PhD Objectives • Describe cells of the epithelium of the nasal cavity, trachea, and bronchioles, including specialized cells such as the olfactory sensory cells, Club (Clara) cells, and Pulmonary Ionocytes. • Provide a general description of airway smooth muscle cells and their relation to respiratory bronchioles, the signaling and molecular mechanisms of bronchoconstriction and bronchodilation. • Provide a general description of alveoli, cellular composition, and the basic functionality of alveolar cells. • Describe the signaling mechanisms and cellular pathways of surfactant production in type II alveolar cells, and the functionality of lamellar bodies. Acronyms • GPCR – G protein coupled receptors • cAMP – cyclic adenosine monophosphate • AC3 – Adenylyl cyclase type 3 • IP3 – Inositol-1,3,5 triphosphate • DAG – Diacylglycerol • PIP2 – Phosphatidylinositol-4,5-bisphosphate • PIP3 – Phosphatidylinositol-3,4,5-triphosphate • PKA – Protein kinase A • PKC – Protein kinase C • ORK – Odorant receptor kinases • • • • • • CNG – Cyclic nucleotide gated channel ASM – Airway smooth muscle PLC – Phospholipase C CaM – Calmodulin MLCK – Myosin-light chain kinase MLCP – Myosin-light chain phosphatase • LB – Lamellar body • SP – Surfactant protein Overview • 1. Nasal Cavities • Olfactory epithelium • Cell types • 2. Airway Epithelia • Cell types • Cystic fibrosis • Bronchoconstriction/dilation • 3. Alveoli • Alveolar Type I and II cells • Surfactant Histology 7th Edition, 2016 Part 1: Nasal Cavity Cells of the Nasal Cavity Epithelium • Respiratory Epithelium: • Similar in cellular composition as trachea • Olfactory epithelium • Specialized sensory cells Junqueira’s Basic Histolog 14th Edition, 2016 Cells of the Olfactory Epithelium • Olfactory sensory cells (receptor cells) • Olfactory neurons • Bipolar neurons • Function of olfactory sensory cells • Interpret odorant signal • Contain olfactory (odorant) receptors • Contain transduction machinery • cAMP or IP3 (second messenger) systems • Supporting cells • Mechanical/structural support • Nutritional support • Basal cells • Stem cells  sensory or supporting cells Part 2: Airway Epithelia Cells of the Respiratory Epithelia Junquiera • Cells are similar in the trachea and bronchi Cells of the Respiratory Epithelia • Basal Cell • Stem cell population • Divide and differentiate • Attach to basement membrane, but do not reach free surface • Columnar ciliated cells • Cilia (microtubules) extending into lumen • Move mucus/debris/pathogens from air passages to pharynx • Attach to basement membrane Cells of the Respiratory Epithelia • Goblet (mucous) cells • Apical side produces protective mucus (mucinogen) layer • Very similar to goblet cells of the intestine • Brush cells (absorptive) • Chemosensing and absorption • Apical microvilli (actin) • Bronchial endocrine cells • Aka enteroendocrine cells • Secrete catecholamines and other peptide hormones Other Cells of the Airway Epithelium • Club cells (formerly Clara cells) • Secrete components of surface-active agent • Defensive mechanisms (lysozymes) • Pulmonary Ionocytes • Recently characterized in 2018 • Regulate salt balance in the lungs • Make up a small percent of airway cells Ci – Ciliated cell C – Club cell Visual Histology, Lea & Febiger, Philadelphia, 1988 Goblet Cells • Characteristics: Approximately 30% of the cell population Non-ciliated Contact with apical lumen and basal lamina Increase in number during chronic irritation Produce mucin glycoproteins (MUC5AC & MUC5B) • Airway mucus: • Made of water and mucins (glycoproteins MUC5AC and MUC5B) • Function: • Trap foreign particles/pathogens/toxic chemicals Histology and Cell Biology 5th Edition, 2020 • • • • • • Club cells Club Cells • Formerly Clara cells • Increase in number from bronchiole to terminal bronchiole • 80% of the epithelial cell population of the terminal bronchioles • Non-ciliated cells Apical Dome • Protection of bronchiolar epithelium • Club cells can proliferate/migrate to replenish alveolar cells (alveolar bronchiolization) • Secrete a surface-active agent (surfactant protein A and D) • Reduces surface tension • Helps prevent collapse of bronchioles Histology and Cell Biology 5th Edition, 2020 • Function Pulmonary Ionocytes • Pulmonary ionocytes • Regulate salt balance • Make up ~1% of airway cells • High levels of CFTR • Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) • • • • Chloride ion channel ABC (ATP-binding cassette) transporter family Conducts Cl- across cell membranes Cystic Fibrosis is caused by a mutation in CFTR Histology and Cell Biology 5th Edition, 2020 Pulmonary Ionocytes and Cystic Fibrosis • Normal Ionocyte • Normal CFTR • Normal Cl- conductance • Abnormal Ionocyte • Defective CFTR • Loss of Cl- conductance • Cells take in larger amounts of H2O from mucus layer • Mucus becomes thick Histology and Cell Biology 5th Edition, 2020 • Normal “balanced” levels of H2O in cells & mucus layer Airway Smooth Muscle and Bronchial Tone Airway Smooth Muscle • Airway smooth muscle (ASM) • Line the airways of the lungs • Trachea through the respiratory bronchioles • Contain GPCRs • Bronchial tone Histology and Cell Biology 5th Edition, 2020 • Regulated by GPCRs Ca2+ and PKA Mediated Effects of Bronchial Tone • MLCK – myosin light chain kinase • MLCP – myosin light chain phosphatase Ca2+/CaM • Bronchoconstriction: GPCR • Activates Gq & IP3/Ca2+ mediated constriction of ASM • Mechanism: • Ca2+/CaM activates MLCK MLCK Relaxation Contraction MLCP • Bronchodilation: β2-AR • Activates Gs & PKA mediated relaxation of ASM • Mechanism: • PKA activates MLCP • Inhibits IP3 pathway PKA Part 3: Alveoli • Alveoli Alveolar Cells • Site of air-blood barrier & gas exchange • Type I • • • • Squamous (thin) Line the surface of alveoli Permit gas exchange Communicate with Type II alveolar cells • Progenitor cells for Type I • Secrete pulmonary surfactant • Brush cells • Few in number • Air quality sensors • Macrophages • Host defense Histology and Cell Biology 5th Edition, 2020 • Type II Alveolar Type II Cells • Alveolar Type II Cells • Surfactant • Oily mixture of proteins and phospholipids • Synthesized in the RER (proteins) & SER (lipids) • Stored in lamellar bodies (secretory granules) Histology and Cell Biology 5th Edition, 2020 • Aka septal cells & secretory cells • Produce surfactant (containing surfactant protein A,B,C, and D) • Polygonal shaped Lamellar Bodies & Pulmonary Surfactant • Lamellar bodies • 150-180/cell • Membranous/secretory granule • Store surfactant • Fuse with cell membrane (exocytosis) • Pulmonary Surfactant: • Lipoprotein complex • Function: • Decrease alveolar surface tension • Prevent collapse of alveoli • Increase lung compliance • Clearance of foreign material Pulmonary Surfactant Proteins • Surfactant: Lipoprotein complex • Phospholipids • Dipalmitoylphosphatidylcholine (DPPC) • Cholesterol • Surfactant proteins A,B,C, and D • Surfactant Proteins (SP): • 4 types: A,B,C, and D • Organize the surfactant layer • Modulate alveolar immune response • SP-A & D: Hydrophilic • SP-A: Regulates synthesis, secretion, and reabsorption of surfactant by AT2 cells • SP-A & D: Part of the innate immune system • SP-B & C: Hydrophobic • SP-B: Helps to form lamellar bodies • SP-B & C: Interact with phospholipids • Maintain (lipid arrangement) of the surfactant layer Homeostasis of Lung Surfactant • Rough ER • Synthesize surfactant proteins • Smooth ER • Synthesize phospholipids • SPs Transport • Golgi • Transported to and stored in lamellar bodies • SP-B plays significant roles in LB formation • Fusion with PM • Once fused, exocytosis occurs • Reuptake of “old” surfactant for recycling • SP-A plays significant roles in secretion and reabsorption of surfactant Purinergic (P2Y2R) is Activated by Alveolar Type I Cells • Alveolar Type I (AEC I) • Stretch sensor • Communicate with Alveolar Type II cells • Use ATP for communication • Alveolar Type II (AEC II) • Produce surfactant J Cell Sci 2011 124: 657-668; doi: 10.1242/jcs.066977 Purinergic Receptor (Purinoceptors) • Purinergic receptors • Receptors that are activated by nucleotides [ATP, ADP], or adenosine • Wide distribution of expression • Types • P1 – G protein coupled • P2Y – G protein coupled • P2X – Ligand-gated channels • Found on Alveolar Type II cells • P2Y receptor • Initiate surfactant production in Alveolar Type II cells Journal of Gen Phys (2016); 148(3): 207 Type II Alveolar Cell Purinergic (P2Y2) Receptor • Surfactant synthesis: • Highly regulated by PKC • Mechanism: • P2Y2R: • GPCR  Gq  PLC • Pathway leads to activation of PKC • PKC: • Stimulates exocytosis of surfactant